CD4 and myeloid sarcoma: T cells can be identified in MS lesions early on and throughout the disease course,3 and are thought to be implicated in the complex pathophysiology of MS next to B cells.4,5 CD4+ T cells are the most abundant cell population in the cerebral spinal fluid (CSF) and were shown to be enriched in MS.6 Pathogenic T cells are considered one of the earliest to breach the blood-brain barrier in nascent demyelinating lesions.7 The animal model experimental autoimmune encephalomyelitis (EAE) serves to understand the transmigration processes of inflammatory T cells into the CNS parenchyma.